For some reason the file is not executable for you. Unfortunately, it is very difficult to give accurate advice for graphical user interfaces. If you are familiar with the Linux console (terminal), please run the installer from there:

I have installed QCAD3 on my laptop which has Ubuntu 11.04, and it runs perfectly (so far), as it ought to, since the RibbonSoft website indicates that QCAD3 has been tested on this platform.

However, QCAD3 does not run on my PC at work with Linux Mint 12 (32-bit), which is based on Ubuntu 11.10. It starts up and shows the initialization splash when I run the qcad shell script from the /opt directory. Then it seems to want to start by showing the main window for less than a second. The window then closes and nothing further happens.

Does anyone have an idea of what I need to do to make QCAD3 work on Linux Mint 12?